\begin{lilypond}
 \language "english"
 
 #(set-global-staff-size 14)
 #(set! paper-alist (cons '("my size" . (cons (* 4.5 in) (* 7 in))) paper-alist))
 
 #(define (rest-score r)
    (let ((score 0)
          (yoff (ly:grob-property-data r 'Y-offset))
          (sp (ly:grob-property-data r 'staff-position)))
      (if (number? yoff)
        (set! score (+ score 2))
        (if (eq? yoff 'calculation-in-progress)
          (set! score (- score 3))))
      (and (number? sp)
           (<= 0 2 sp)
           (set! score (+ score 2))
           (set! score (- score (abs (- 1 sp)))))
      score))
 
 
 #(define (merge-rests-on-positioning grob)
    (let* ((can-merge #f)
           (elts (ly:grob-object grob 'elements))
           (num-elts (and (ly:grob-array? elts)
                          (ly:grob-array-length elts)))
           (two-voice? (= num-elts 2)))
      (if two-voice?
        (let* ((v1-grob (ly:grob-array-ref elts 0))
               (v2-grob (ly:grob-array-ref elts 1))
               (v1-rest (ly:grob-object v1-grob 'rest))
               (v2-rest (ly:grob-object v2-grob 'rest)))
          (and
            (ly:grob? v1-rest)
            (ly:grob? v2-rest)          
            (let* ((v1-duration-log (ly:grob-property v1-rest 'duration-log))
                   (v2-duration-log (ly:grob-property v2-rest 'duration-log))
                   (v1-dot (ly:grob-object v1-rest 'dot))
                   (v2-dot (ly:grob-object v2-rest 'dot))
                   (v1-dot-count (and (ly:grob? v1-dot)
                                      (ly:grob-property v1-dot 'dot-count -1)))
                   (v2-dot-count (and (ly:grob? v2-dot)
                                      (ly:grob-property v2-dot 'dot-count -1))))
              (set! can-merge
                (and 
                  (number? v1-duration-log)
                  (number? v2-duration-log)
                  (= v1-duration-log v2-duration-log)
                  (eq? v1-dot-count v2-dot-count)))
              (if can-merge
                ;; keep the rest that looks best:
                (let* ((keep-v1? (>= (rest-score v1-rest)
                                     (rest-score v2-rest)))
                       (rest-to-keep (if keep-v1? v1-rest v2-rest))
                       (dot-to-kill (if keep-v1? v2-dot v1-dot)))
                  ;; uncomment if you're curious of which rest was chosen:
                  ;;(ly:grob-set-property! v1-rest 'color green)
                  ;;(ly:grob-set-property! v2-rest 'color blue)
                  (ly:grob-suicide! (if keep-v1? v2-rest v1-rest))
                  (if (ly:grob? dot-to-kill)
                    (ly:grob-suicide! dot-to-kill))
                  (ly:grob-set-property! rest-to-keep 'direction 0)
                  (ly:rest::y-offset-callback rest-to-keep)))))))
      (if can-merge
        #t
        (ly:rest-collision::calc-positioning-done grob))))
 
 \paper {
   #(set-paper-size "my size")
 }
 
 
 
 
 
 \parallelMusic #'(soprano alto tenor bass) {
   g8.( a16) g8 e4.       | e8.( f16) e8 e4.         | r4.          r8 g8 g | r4.         r8 c,8 c |
   g8.( a16) g8 e4.       | e8.( f16) e8 e4.         | r4.          r8 g8 g | r4.         r8 c8 c |
   d'4 d8 b4.             | r8 d8 e f( e d)          | r8 f8 g a( g f)      | r8 c8 c c4.         |
   c4 c8 g4.              | r8 c8 d e( d c)          | r8 e8 f g( f e)      | r8 c8 c c4.         |
   \break
   
   \slurDashed a4 a8 c8.( b16) a8   |
   \slurDashed r8 c8 f a8.( g16) f8 |
   \slurDashed r8 f8 f f( g) a      |
   \slurDashed r8 f8 f f f f          |
   g8.( a16) g8 e4.     | e8.( f16) e8 c4.       | c8( c) c g4.        | c'8( c) c c,4.    |
   a4 a8 c8.( b16) a8   | r8 c8 f a8.( g16) f8   | r8 f8 f f( g) a    | r8 f8 f f f f     |
   g8.( a16) g8 e4.     | e8.( f16) e8 c4.       | c8( c) c g4.      | c'8 c c, c4. |
 
 
   \slurSolid d'4 d8 f8. d16 b8      |
   \slurSolid r8 d8 g b a g            |
   \slurSolid r8 b8 b d c d                  |
   \slurSolid r8 g'8 g g g f       |
   c4.( e4.)               | g4. e4.                  | g,4. c               | e'4. c              |
   c8.( g16) e8 g8. f16 d8 | r8 e16( d) c8 b8. a16 b8 | r8 c c g g f         | r8 g'8 g g g, g     |
   c2.                     | c2.                      | e2.                  | c2.                 |
 }
 
 \score {
   \header{
   }
 
   \new ChoirStaff  \with {
     \override RestCollision.positioning-done = #merge-rests-on-positioning
   } <<
     \new Staff = "female" {
       \time 6/8
       \key c \major
       \new Voice = "women" <<
         \relative c'' {
           {\voiceOne \soprano}
         }
         \new Voice = "altos" {\relative c' { \voiceTwo \alto }}
       >>
     }
     \new Lyrics {
       \lyricsto "women" {
         \set stanza = #"1. "
         \skip 1 \skip 1 \skip 1 \skip 1 \skip 1 \skip 1
         All is calm, __ __ __ all is bright __ __ __
         Round yon 
         Vir -- gin
 
         \set ignoreMelismata = ##t
         mo -- ther
 
         and child,
         Ho -- ly
         
         in -- fant
         
         so
         
         ten -- der and mild,
         \unset ignoreMelismata
 
         Sleep in hea -- ven -- ly peace, __
         Sleep __ in hea -- ven -- ly peace.
       }
     }
     \new Lyrics {
       \lyricsto "women" {
         \set stanza = #"2. "
         Si -- lent Night, Ho -- ly Night,
 
         Shep -- herds quake, __ at the sight; __
         Glo -- ries stream __ from 
 
         \set ignoreMelismata = ##t
         hea -- ven
         \unset ignoreMelismata
 
         a -- far, Heav'n -- ly hosts __ sing
 
         \set ignoreMelismata = ##t
         Al -- le -- lu -- ia;
         \unset ignoreMelismata
 
         Christ, the Sa -- vior is born, __ Christ, __ the Sa -- vior, is born.
       }
     }
     \new Lyrics {
       \lyricsto "women" {
         \set stanza = #"3. "
         \skip 1 \skip 1 \skip 1 \skip 1 \skip 1 \skip 1
         Son of God, __ love's pure light __
         Ra -- diant beams from
 
         \set ignoreMelismata = ##t
         thy ho -- ly face,
         \unset ignoreMelismata
 
         With the dawn of
         
         \set ignoreMelismata = ##t
         re -- deem -- ing grace,
         \unset ignoreMelismata
 
         Je -- sus, Lord, at thy birth, __
         Je -- sus, Lord, at thy birth.
       }
     }
 
     \new Staff = "male" {
       \clef "bass"
       \relative c' {
         \time 6/8
         \key c \major
         \new Voice = "men" <<
           {\voiceOne \tenor}
           \new Voice = "basses" { \voiceTwo \bass }
         >>
       }
     }
     \new Lyrics {
       \lyricsto "men" {
         Si --  lent, Ho -- ly,
       }
     }
   >>
 
   \layout {
     indent = 0.0\cm
     \context {
       \Lyrics
       \override LyricText #'font-size = #-2
     }
   }
   \midi { }
 }
 
 \version "2.18.2"  % necessary for upgrading to future LilyPond versions.
 \end{lilypond}